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Saturday, June 15, 2013

Arecibo Radar Sees Asteroid 1998 QE2 and Moon

Arecibo Observatory catches the most detailed radar images ever of asteroid 1998 QE2 and its newly discovered moon as they safely pass our planet. Arecibo Observatory continues to take radar images of asteroid 1998 QE2 and its moon as the space rock sails safely passed earth this week. The images show a dark cratered asteroid 3 kilometers across (1.9 miles) with a companion moon 750 meters (2,500 feet) in size. The asteroid and its moon passed 6 million kilometers (3.75 million miles) from earth, far enough from our planet not to worry, close enough to study this rocky world with the most sensitive radar telescope in the world, the U.S. National Science Foundation's Arecibo Observatory in Puerto Rico. "Asteroid QE2 has no chance of hitting earth," said USRA's Dr. Michael Nolan, head of the asteroid radar group at Arecibo Observatory who took the images.

Arecibo Observatory and the complementary Goldstone Solar System Radar in California run by NASA's Jet Propulsion Laboratory are unique among telescopes on earth for their ability to resolve features on asteroids, when optical telescopes on the ground would see these rocks as simple points of light. "We transmit powerful radio waves at passing asteroids," said Nolan. "Arecibo is a thousand times more powerful than your microwave oven." Sensitive radio receivers collect radio signals reflected from the asteroids and computers turn the radio echoes into images that show features such as craters and the smaller moon. The moon appears brighter than the asteroid as it is rotating more slowly; thus, its Doppler echoes compress along the Doppler axis of the image and appear stronger.

Radar image of Asteroid 1998 QE2 taken on June 7, 2013 as the asteroid and its moon safely passed Earth. Image credit: Arecibo Observatory/NASA/Ellen Howell

Of the asteroids that come close to Earth, approximately one out of six have moons. Dr. Patrick Taylor, a USRA research astronomer at Arecibo, remarked that "QE2's moon is roughly one-quarter the size of the main asteroid," which is a lumpy, battered world in the inner part of our solar system. "Similarly, our moon is also approximately one-fourth the size of our planet."

QE2's moon will help scientists determine the mass of the main asteroid and what minerals make up the asteroid-moon system. "Being able to determine its mass from the moon helps us understand better the asteroid's material," said Dr. Ellen Howell, a USRA research astronomer at Arecibo Observatory who took both radar images of the asteroid at Arecibo and optical and infrared images using the Infrared Telescope Facility in Hawaii. While the optical images do not show detail of the asteroid's surface, like the radar images do, instead they allow for measurements of what it is made of. Howell said, "What makes this asteroid so interesting, aside from being an excellent target for radar imaging, is the color and small moon."

"Asteroid QE2 is dark, red, and primitive - that is, it hasn't been heated or melted as much as other asteroids," continued Howell. "QE2 is nothing like any asteroid we've visited with a spacecraft, or plan to, or that we have meteorites from. It's an entirely new beast in the menagerie of asteroids near Earth."

The provisional designation "1998 QE2" reflects the mid-August 1998 discovery date of this asteroid and is not related to the Queen Elizabeth II ocean liner, though a similarity of the asteroid's name to that of a cruise ship makes for interesting size comparisons. Arecibo astronomer Rhys Taylor said, "The moon is twice the length of the Queen Elizabeth II ocean liner, while the asteroid is nine times the length. Twenty-nine QE2 ships would fit around the circumference of asteroid QE2, plus or minus a ship."

USRA's Michael Nolan led the radar observations of QE2, with Ellen Howell, Patrick Taylor, Alessondra Springmann, Sean Marshall of Cornell University, and Mariah Law of Embry-Riddle Aeronautical University, in collaboration with the Near-Earth Object radar team at NASA/JPL and Goldstone Observatory in California. Observations continued through the morning of June 13, 2013.

Located in Puerto Rico, the Arecibo Observatory is home to the world's largest and most sensitive single-dish radio telescope, and dedicates hundreds of hours a year of its telescope time to improving our knowledge of near-Earth asteroids.